Reducing knock in an engine combustion engine, has been a major challenge over the past decade and will continue to be a challenge in the future in part due to the continuing stringent emission requirements for engine emissions and control systems related thereto. Attempts to reduce knock often include an approach that embraces one in a series of methods such as Direct injection (DI), engine gas recirculation [EGR] dilution, or spark retarding (Spark Retard or “SR”). Knock is widely understood to be an issue that arises with respect to increased or peak cylinder temperatures in an engine above which knocking may become more prevalent.
However, reducing knock tendency in spark-ignited (SI) engines, in particular, can limit the torque output of the engine as the charge/air mixture is often restricted. While each approach may have some benefit for specific situations and certain unique operating environments, each often has many disadvantages when considered across the operating environment of most engines.
For instance, while DI may allow more accurate control over fuel metering (the amount of fuel injected) and injection timing (exactly when the fuel is introduced into the cylinder), engines able to take better benefit of such a limited approach only because they are rugged in design, utilize high pressure systems and are therefore often very expensive and complex. Similarly, the DI event injects secondary level of fuel close to the injection timing event in an attempt to suppress the knock, and the timing of such an event may not be ideal in certain operational ranges.
Similarly, for EGR, while adding EGR to the air flow rate of an engine is more beneficial than displacing some of the inlet air and also allows exhaust NOx emissions to be reduced substantially, EGR takes time and also effectively reduces the combustion rate thereby making stable combustion often a challenge. Another variation often deployed in SI engines to reduce the knock is to retard the spark; however disadvantages in this sole approach include increased hydrocarbon output and heightened NOx emissions. Further, during a spark retarding (SR) event efficiency of the engine can be sacrificed greatly and in some cases, certain operational regions of combustion may fail. Each of these methods has a similar objective of reducing peak in-cylinder temperatures.
As each of these approaches, or methods of actuation, has disadvantages to the performance of the engine, with respect to transient times, and in achieving the objective of reducing knock across an operating environment of an engine, accordingly, an approach that is able to accommodate knock reduction across an engine's operating environment using a plurality of actuation approaches at opportune times with respect to the operational state and performance characteristics of the engine, is needed. The present invention is directed towards meeting these and many other needs.